Conventionally, a base station is known that performs adaptive array antenna (hereinafter referred to as “AAA”) transmission according to the combined weight for each diversity branch obtained upon AAA reception. By using this technique, the reception electric field strength increases at a mobile station in downlink, and interference against mobile stations connected to another base station which has been interference source upon reception decreases.
In a system employing AAA transmission, cases might occur where nondirectional communication and directional communication both exist (for example, see Patent Document 1.) In the case where nondirectional signals as well as directional signals are transmitted—particularly in the case where AAA is used in downlink—pilot signals and control signals generally required for all terminals are transmitted without directivity, and dedicated data for each terminal is transmitted with directivity. Hereinafter, control signals required for all terminals transmitted without directivity will be referred to as nondirectional transmission signals, and dedicated data for each terminal transmitted with directivity will be referred to as directional transmission signals. In view of received signal level at each terminal, the possibility is larger that received signal level increases in the case where directional signals are received than the case where nondirectional signals are received. Furthermore, in the case of a system where data for a terminal is transmitted in bursts, while nondirectional signals are received at low power level, suddenly directional signals at large power level are received.
FIG. 1A and FIG. 1B illustrate relationship between the received power level and the received timing of conventional nondirectional received signals #11, #13 and a directional received signal #12. As shown in FIG. 1A, processing of increasing the dynamic range starts for the first time at time t10 when directional received signal #12 is received. By this means, a dynamic range including the power level of directional received signal #12 is set at time t11.
Patent Document 1: Japanese Patent Application Laid-Open No. 2003-134025